A fuel cell is a power generation system for generating electric energy by electrochemically reacting hydrogen and oxygen. According to the type of electrolyte used, a fuel cell can be characterized as a phosphoric acid fuel cell, a molten carbonate fuel cell, a solid oxide fuel cell, a polymer electrolyte fuel cell, an alkaline fuel cell, etc. These respective fuel cells are generally operated based on the same principle, but are different in view of types of fuels used, operating temperatures, catalysts and electrolytes, etc. Among the different types, the polymer electrolyte membrane fuel cell (PEMFC) has the advantages of remarkably high output characteristics, low operating temperature characteristics, and rapid starting and responding characteristics over other fuel cells, and is widely applicable as a mobile power source for portable electronic equipment, and automobiles, as well as a distributed power source in homes and public buildings, etc.
Since hydrogen has the best reactivity in the electrochemical oxidation reaction at the anode electrode, and does not exhaust polluting substances because it generates water after reacting with oxygen, it is the most suitable substance as a fuel for a fuel cell. However, since hydrogen rarely exists in a readily available form, it must often be obtained by reforming other raw materials. For example, hydrogen can be obtained from hydrocarbon-based fuels, such as gasoline, diesel, methanol, ethanol, natural gas, etc., through a reformer. Hydrogen can also be obtained by reforming a fuel such as butane which is readily available on the market and can be provided in pressurized cans. Therefore, supposing that a butane can is used as a fuel supply for a fuel cell, it has the advantage that the hydrogen containing fuel can be easily obtained, and fuel can be supplied by using the internal pressure of the butane can, without using a compressor.
Meanwhile, in the reformer, the range of the reaction temperature to be required in each reaction zone differs according to the reacting catalysts installed in each reaction zone. For example, the range of the reaction temperature in a steam reforming (SR) reaction is different depending on the reforming raw material, i.e., approximately from 600° C. to 900° C. for hydrocarbon-based fuels such as butane, and approximately from 250° C. to 400° C. for a fuel such as methanol. The range of the reaction temperature in a water gas shift (WGS) reaction, one of the processes for removing carbon monoxide, is approximately 200° C. to 350° C., and the range of the reaction temperature in a preferential CO oxidation (PROX) reaction is approximately 100° C. to 250° C. The range of the reaction temperatures in each reaction zone in the reformer in decreasing order is: the reforming reaction unit, the shift reaction unit (or water-gas-shift reaction unit), and the preferential CO oxidation unit.
As described above, in a reformer that is reforming hydrocarbon-based fuel such as butane, it is difficult to properly control the reactions in each reaction zone because the differences in the reaction temperatures of each reaction zone are larger than for a reformer using methanol fuel. Therefore, in a reformer using a fuel such as butane, there is a need to have rapid preheating with high thermal efficiency while properly controlling the reaction temperatures of each reaction zone.